[Merged by Bors] - Do not return empty address on not found

[fasmat]

Motivation

Instead of returning an empty account when an address wasn't found in the DB return sql.ErrNotFound

Description

At the moment Latest and Get always return a types.Account{} and nil error if the given address wasn't found. With this change the two functions instead return sql.ErrNotFound as error.

Test Plan

existing tests pass

TODO

• [x] Explain motivation or link existing issue(s)
• [x] Test changes and document test plan
• [x] Update documentation as needed
• [x] Update changelog as needed

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.9%. Comparing base (f4de865) to head (72a9e80). Report is 2 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #6463 +/- ## ======================================= Coverage 79.9% 79.9% ======================================= Files 353 353 Lines 46424 46432 +8 ======================================= + Hits 37122 37144 +22 + Misses 7197 7186 -11 + Partials 2105 2102 -3 ```

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[fasmat]

bors merge

[spacemesh-bors[bot]]

Pull request successfully merged into develop.

Build succeeded:

• ci-status
• systest-status